The present invention relates to an apparatus for producing thin solidified alloy pieces and a method for producing thin solidified alloy pieces with this apparatus. For casting a variety of alloys, in particular for cooling and solidifying into thin pieces a melt of an alloy, such as a rare earth-containing alloy, that can be used for producing magnets, hydrogen storage alloys, alloys for anode of secondary batteries, or catalysts, flow of an alloy melt is supplied from a container via a flow stabilizing means such as a tundish onto a cooling roll. In such process, this apparatus can automatically provide a constant flow of the alloy melt from the container to produce thin solidified alloy pieces of a uniform thickness.
In alloy casting, there are generally known two methods for cooling and solidifying an alloy melt into thin pieces: namely, (1) directly guiding an alloy melt onto a cooling roll; and (2) guiding an alloy melt via a flow stabilizing means such as a tundish onto a cooling roll. The latter method (2) provides stabilization of the flow of the alloymelt, and control of the temperature of the alloy melt as well as the angle of the alloy melt to be guided onto the cooling roll. In method (2) , the alloy melt is usually accommodated in a container having a cylindrical or prismatic interior configuration with a top opening, and is made to flow over a portion of the edge of the top opening when the container is gradually tilted for guiding the alloy melt to the flow stabilizing means.
In this step, it is required to control the outflow of the alloy melt in order to keep the thickness of the resulting solidified pieces substantially uniform for achieving fixed and improved alloy properties.
For instance, controlling the flow rate of the alloy melt, which changes with the tilt angle of the container, to provide continuous and constant flow is quite difficult. The change in outflow of the alloy melt from the container is briefly explained below with reference to the drawings.
FIG. 3 illustrates how an alloy melt flows out of a container having cylindrical interior configuration with a circular top opening, in views seen horizontally from the front side of the top opening of the tilted container. FIG. 3(A) shows the state of container 1' at the beginning of tilting, wherein the flow rate of alloy melt 6 is relatively low. FIG. 3(B) depicts the state of container 1' at a tilt angle of about 45 degree, wherein the flow rate of alloy melt 6 is high. FIG. 3(C) indicates the state of container 1' at a tilt angle of about 90 degree, wherein little alloy melt 6 remains in container 1' so that the flow rate thereof is low.
In this way, the flow rate of the alloy melt changes with the tilt angle of the container. Consequently, if the tilting angular velocity of the container is fixed, the flow rate cannot be kept constant. To solve this problem to provide constant flow of the alloy melt from the container, there are proposed methods for controlling the flow rate of the alloy melt utilizing so-called feedback. For example, the control may be achieved by detecting the flow rate by a sensor, and contrasting the detected rate with the desired rate to decide the tilting angular velocity point by point; or by receiving the flow of the alloy melt from the container first in a tundish having a nozzle at its end, detecting the change in weight of the overall tundish by a load cell, and tilting the container when the detected value falls behind the predetermined lower limit, or stopping tilting the container when the detected value exceeds the predetermined upper limit.
In the former controlling method wherein the tilting angular velocity is decided point by point utilizing feedback, detection of the rate of continuously flowing alloy melt is required, which is difficult to carry out with accuracy and requires sensors with special equipment. In addition, since the decision of the tilting angular velocity is based on the detected flow rates, the control is likely to be deficient due to inadequate detection of the flow rate. To avoid this problem, the sensors are required to have high accuracy and durability, and controlling computer is demanded to have markedly high speed processing capacity, also causing economical problems. Also, the alloy melt of extremely high temperature necessitates heat resistance of the sensors. On the other hand, in the latter controlling method utilizing feedback from the load cell, not a little amount of alloy melt should be retained in the tundish, which inevitably requires large scale facilities. Moreover, in order to prevent unreasonable temperature drop of the alloy melt retained in the tundish, an apparatus for heating the alloy melt should be installed additionally.
Conventionally known flow stabilizing means for guiding a substantially constant flow of an alloy melt from the container onto the cooling roll include a tundish having a guiding passage for guiding the alloy melt toward the cooling roll and a nozzle for allowing the alloy melt from the guiding passage to flow down onto the cooling roll. The nozzle may be provided with a variety of passages for stabilizing the flow of the alloy melt. Upon starting a new flow cycle, the nozzle on such flow stabilizing means may sometimes be clogged up with the alloy melt remaining in the nozzle at the completion of the previous flow cycle. This is particularly true with a nozzle having the variety of passages for flow stabilization. Therefore, development of flow stabilizing means which will not be clogged up is also demanded.